The present invention relates to a composition based on polypropylene homopolymer or copolymer (PP), and on an ethylene/alkyl acrylate copolymer with a linear or branched alkyl group containing a number of carbon atoms greater than or equal to 6, preferably equal to 8, this composition acting as impact modifier for the polypropylene. The alkyl acrylate is preferably 2-ethylhexyl acrylate or n-octyl acrylate or a blend of 2-ethylhexyl acrylate and octyl acrylate. This impact-modified PP composition exhibits good impact strength properties, especially at low temperatures, compared with unmodified PPs or with PPs modified by ethylene/methyl acrylate (EMA) or ethylene/butyl acrylate (EBA) copolymers. This composition may optionally include reinforcing fillers.
These compositions are useful for manufacturing parts which have to exhibit good impact strength at room temperature and at low temperatures. These compositions may serve for manufacturing inter alia bumpers, tubes or pipes, panels or dashboards for motor vehicles, tarpaulins and membranes, and sheets or films for the interior furnishing of motor vehicles.
Document U.S. Pat. No. 5,272,210 discloses a composition comprising a propylene/ethylene copolymer and an ethylene/alkyl acrylate copolymer. The alkyl acrylate may be ethyl acrylate (EEA), methyl acrylate (EMA) and butyl acrylate (EBA), the latter two esters being preferred. The examples given in that patent are made with methyl acrylate. The films produced with these compositions have good sealing and flexibility properties at low temperatures.
Document U.S. Pat. No. 3,433,573 relates to a composition comprising a blend of predominantly propylene-based polypropylene and of an ethylene/vinyl acetate (EVA) copolymer for manufacturing sheets, films and moulded articles with improved coloration and properties at low temperatures, such as flexibility and strength.
Document U.S. Pat. No. 3,555,110 discloses polymer compositions having propylene and ethylene blocks or having propylene and 1-butene blocks which are blended with etheylene/ethyl acrylate (EEA) copolymers or with ethylene/vinyl acetate (EVA) copolymers, these compositions exhibiting improved impact strength properties at low temperatures.
Homopolymer polypropylene does not have a good impact strength. Ethylene/propylene random copolymers or ethylene-propylene block copolymers exhibit better impact strength values thanks to the EPR part generated during the polymerization phase. However, these products have limitations as it is not always possible for the necessary amounts of EPR (ethylene propylene rubber) to be synthesized in situ. These block copolymers without the EPR part prove to have a low impact strength in applications at low temperatures.
Copolymers of the ethylene/acrylic ester, ethylene/methyl acrylate and ethylene/butyl acrylate (EMA, EBA) type are impact modifiers for PP but do not make it possible to obtain impact strength values comparable with the values from EPRs or EPDMs.
We have now found an impact modifier for polypropylene based on ethylene/alkyl acrylate, preferably 2-ethylhexyl acrylate, abbreviated to 2EHA in the rest of the text, or n-octyl acrylate, making it possible to obtain impact strength values higher than those obtained with conventional copolymers of the EMA or EBA type and especially good low-temperature impact strength.
The subject of the invention is a composition comprising polypropylene homopolymer or copolymer (A), and an ethylene/alkyl acrylate copolymer as impact modifier with a linear or branched alkyl group containing a number of carbon atoms greater than or equal to 6, preferably greater than or equal to 7.
According to one embodiment of the composition, the alkyl acrylate is 2-ethylhexyl acrylate, n-octyl acrylate or a blend thereof.
According to one embodiment of the composition, this comprises at least one polyethylene (B) taken from the group comprising LDPE, HDPE, LLDPE, VLDPE, polyethylene obtained by metallocene catalysis, EPR and EPDM elastomers, polyethylene/EPR or EPDM blends, ethylene/alkyl (meth)acrylate copolymers and ethylene/vinyl acetate copolymers. According to one embodiment of the composition, the ethylene/vinyl acetate copolymers are ethylene/vinyl acetate/maleic anhydride terpolymers.
According to one embodiment of the composition, the ethylene/alkyl (meth)acrylate copolymers are ethylene/alkyl (meth)acrylate/maleic anhydride terpolymers, ethylene/alkyl (meth)acrylate/glycidyl methacrylate terpolymers or ethylene/alkyl (meth)acrylate/(meth)acrylic acid terpolymers.
According to one embodiment of the composition, the latter comprises between about 1 and 60%, preferably 1 to 40%, by weight of ethylene/alkyl (meth)acrylate copolymer.
According to one embodiment of the composition, the latter comprises at least one additive taken from the group comprising stabilizers, antioxidants, plasticizers, lubricants, carbon black and colouring agents.
According to one embodiment of the composition, the latter includes fillers.
The subject of the invention is also the use of the composition described above for manufacturing sheets, membranes, films, tarpaulins, dashboards for motor vehicles, tubes or pipes, panels and bumpers requiring good thermomechanical strength over a wide range of temperatures.
As regards the polypropylene (A), this is a homopolymer or copolymer.
As comonomers, mention may be made of:
alpha-olefins, advantageously those having from 3 to 30 carbon atoms.
Examples of alpha-olefins having from 3 to 30 carbon atoms has possible comonomers comprise ethylene, 1-butene, 1-pentene, 3-methyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-hexene, 5-methyl-1-hexene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene, 1-triacontene, styrene, allylbenzene, allylcyclohexane, allylcyclopentane and vinylcyclohexane. These alpha-olefins may be used by themselves or as a mixture of two or more of them.
dienes, such as for example 1,4-hexadiene.
The polypropylene (A) may also be a propylene/alpha-olefin block copolymer. In general, the block polymers are prepared by polymerizing an alpha-olefin and then adding, to the reaction mixture, another alpha-olefin, one of the two alpha-olefins being propylene. In the case of a polypropylene copolymer having propylene and ethylene blocks, the polymerization leads to the formation of block polymers containing segments of propylene units or polypropylene segments and segments of ethylene units or polyethylene segments. These block polymers have in general only two segments in their chain and consist of a polypropylene segment comprising about 50% to 99% by weight and a polyalpha-olefin segment, other than polypropylene, comprising approximately 50% to 1% by weight.
The present invention relates to PPs obtained by Ziegler-Natta catalysis and to PPs obtained by metallocene catalysis. As regards the PPs obtained by metallocene catalysis, mention may be made of syndiotactic and isotactic PPs.
Good low-temperature impact properties are obtained with relatively small amounts of ethylene/alkyl acrylate copolymer with a linear or branched alkyl group containing a number of carbon atoms greater than or equal to 6, preferably greater than or equal to 7 in the compositions according to the invention.
The compositions according to the invention comprise about 1 to 60%, preferably 1 to 40%, by weight of ethylene/alkyl acrylate copolymer and about 99 to 35% by weight of polypropylene homopolymer or copolymer (A), and optionally at least one other polymer (B), the total of the percentages being 100%.
The ethylene/alkyl acrylate copolymer comprises about 55 to 99% by weight of ethylene and about 45 to 1% by weight of alkyl acrylate with the total of the percentages making 100%.
The compositions according to the invention may include, in addition to the polypropylene (A) and the ethylene/alkyl acrylate copolymer, at least one other polymer (B) chosen from polyethylene homopolymers or copolymers.
As comonomers for the polyethylene (B), mentioned may be made of:
alpha-olefins, advantageously those having from 3 to 30 carbon atoms. Examples of alpha-olefins having 3 to 30 carbon atoms as possible comonomers comprise propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene and 1-triacontene. These alpha-olefins may be used by themselves or as a mixture of two or more of them;
unsaturated carboxylic acid esters such as, for example, alkyl (meth)acrylates, the alkyls possibly having up to 24 carbon atoms. Examples of alkyl acrylates or methacrylates are especially methyl methacrylate, methyl acrylate, ethylmethacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, gycidyl methacrylate and n-octyl acrylate;
vinyl esters of saturated carboxylic acids such as, for example, vinyl acetate or vinyl propionate;
unsaturated epoxides. Examples of unsaturated epoxides are especially aliphatic glycidyl esters and ethers such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidyl acrylate, glycidyl methacrylate and alicyclic glycidyl esters and ethers such as 2-cyclohex-1-yl glycidyl ether, diglycidyl cyclohexene-4-5-dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylate and diglycidyl endo-cis-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate;
unsaturated carboxylic acids, their salts and their anhydrides. Examples of unsaturated dicarboxylic acid anhydrides are especially maleic anhydride, itaconic anhydride, citraconic anhydride and tetrahydrophthalic anhydride;
dienes such as, for example, 1,4-hexadiene.
The ethylene copolymer (B) may comprise several comonomers.
Advantageously, the polymer (B), which may be a blend of several polymers, comprises at least 50 mol % and preferably 75 mol % of ethylene. The density of (B) may be between 0.86 and 0.98 g/cm3. The MFI (melt flow index at 190xc2x0 C./2.16 kg) is advantageously between 1 and 1000 g/10 min.
As examples of polymers (B), mention may be made of:
low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and very low-density polyethylene (VLDPE);
polyethylene obtained by metallocene catalysis, that is to say polymers obtained by the copolymerization of ethylene with an alpha-olefin such as propylene, butene, hexene or octane, in the presence of a mono-site catalyst generally consisting of a zirconium or titanium atom and two alkyl cyclic molecules linked to the metal;
EPR (ethylene/propylene rubber) elastomers, EPDM (ethylene/propylene/diene) elastomers, blends of polyethylene with an EPR or an EPDM;
ethylene/alkyl (meth)acrylate copolymers possibly containing up to 60%, and preferably 2 to 40%, by weight of alkyl (meth)acrylate;
ethylene/alkyl (meth)acrylate/maleic anydride or ethylene/alkyl (meth)acrylate/glycidyl methacrylate or ethylene/alkyl (meth)acrylate/(meth)acrylic acid terpolymers possibly containing from 0 to 60% and preferably from 2 to 40% by weight of alkyl (meth)acrylate, the amount of maleic anydride or of glycidyl methacrylate or of (meth)acrylic acid (depending on the terpolymer chosen) being between 0 and 10% and preferably between 0.2 and 6% by weight, and ethylene/vinyl acetate/maleic anydride copolymers, the proportions of alkyl (meth)acrylate and of maleic anydride being in this case the same as in the case of the above ethylene/alkyl (meth)acrylate/maleic anydride copolymer;
ethylene/glycidyl methacrylate, ethylene/acrylic acid and ethylene/methacrylic acid copolymers.
The compositions according to the invention may also contain various additives such as stabilizers, antioxidants, plasticizers, lubricants, carbon black or colouring agents normally used in polyolefins. They may also contain fillers such as talc, mica, kaolin, wollastonite and glass fibres or spheres. Such additives and/or fillers may be added to the composition according to the invention in necessary and sufficient amounts known to those skilled in the art, without modifying the impact properties of the blend thus obtained.